Sensitive pressure-responsive device



p 1965 J. E. LINDBERG, JR 3,205,329

SENSITIVE PRESSURE-RESPONS IVE DEVICE Original Filed July 15, 1961 3/ a'5 0 as I f M? 34 INVENTOR. 0 5 3 Joy/v f Z/NDBfRG, Je

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United States Patent 3 Claims. (Cl. 200-140) This application is adivision of application Serial No. 126,437, filed July 13, 1961.

This invention relates to an improved apparatus for heat detection andespecially fire detection. More particularly it relates to a novelresponder means.

The present invention is an improvement of the apparatus described andclaimed in my copending application, Serial No. 102,622, filed Apr. 10,1961, now abandoned. Thatapplication provides a novel non-electricheat-detecting element or sensor located in a heat-detection zone andconnected outside the zone to an electrical warning or corrective systemby a novel instrument called a responder. The sensor may be filamentaryalong, very-narrow-diameter, hollow tube, which may extend along a line,varound a circle, or along any desired path and for practically anydesired length. Also, the actual alarm or heat-conduction indicator canbe connected to the responder by a wire of practically any desiredlength. For example, the heat-detecting sensor may be inside a house,theresponder just outside the house, and the indicator at the fire station.Or, the non-electric heat-detecting sensor may be in zone 1 of anaircraft engine ahead of a fire wall, the responder may be behind thefire wall, and the indicator may be on the aircraft instrument panel. I

' An object of this invention is to provide a responder having unusuallygood responsecharacteristics and, in particular, an accelerated snapaction. Other objects and advantages of the invention will appearfromthe following description of some illustrattive embodiments thereof. 7 i

In the drawings:

' FIG. 1 is a diagrammatic fragmentary view in perspective of a portionof an aircraft containing a fire-detection and warning device embodyingthe principles of 'this invention.

FIG. 2' is an enlarged view in elevation and partly in section of a firedetection system as used in FIG. 1, showing the responder, a heatdetection sensor broken in the middle in order to conserve space, and acircuit diagram.

FIG. 3 is a further enlarged view in elevation and in section of thenovel responder of FIG. 2, showing also a portion of the sensor.

FIG. 4 is a greatly enlarged View in elevation and in section of aportion of one preferred form of heat-detection sensor.

i As shown in FIG. 1, the fire-detection system with which thisinvention may be used preferably. comprises (1) a non-electric detectionmeans, preferably in the form of a generally filamentary sensor A ofsome desired length, (2) a responder B, and (3) an electrical circuit C.The function of the sensor A is to actuate the responder B, which inturn actuates the electrical circuit C. .Thus, the sensor A constitutesa heat-to-pressure' transducing means, while the sensor A and theresponder B, considered together, comprise a heat-to-electric-cur-3,205,329 Patented Sept. 7, 1965 in the responder B. The responder B isa type of pressure-actuated electrical switch that opens or closes inresponse to the pressure changes induced by the response of the sensor Ato heat. The electrical circuit C may be a warning circuit or a remedialcircuit.

The system of this invention has many features especially suitable touse in aircraft. Just to give a general picture that can be referred tofrom time to time, FIG. 1 presents an aircraft 20 in which two systemsof this invention are installed. Two sensors A are used, one for each oftwo engine naoelles 21, -22 of this airplane 20. The sensors A aredisposed at critical locations in the nacelles 21, 2,2, usually aroundthe engines, and the responders B are mounted on the fire walls 23, 24.The circuits C include conductors 25, 26 leading to respective lights27, 28 on an instrument panel. Fire at either engine nacelle 21 or 22heats the sensor A therein and causes its associated responder B toclose its associated circuit C, thereby lighting the light 27 or 28.

The sensor A includes a narrow-diameter metal tube D of constantcross-sectional area and of any desired length. Within this tube D ismeans E responsive to the temperature of the tube D for varying thepressure inside the tube or enclosure D. This means B may also be termeda transducing agent or a gas-transfer or gas.- emitting agent. Theenclosure D is gas-tight and its only opening is connected to theresponder B, which itself defines a closed chamber connected to theenclosure D. An alteration of the internal pressure within the enclosureD therefore affects the internal pressure within the responder B.

The sensor with which this invention is used preferably employs thetransducing agents E that retain gas at low temperature and emit gasprogressively over a wide range of elevated temperatures. They are setout in detail in my copending application, Serial No. 102,622, nowabandoned, to which reference may be had for complete details. Thesetransducing agents E release or emit large volumes of gases or vaporswhen elevated to a temperature sought to be detected and take them upagain when the temperature is reduced.

Among suitable materials for the transducing agent E are many metallichydrides. With the alkali and alkaline earth metals, i.e., groups Ia andII-a of the periodic table, hydrogen forms stoichiometric compounds suchas sodium hydride and calcium hydride. These are ionic in behavior, withhydrogen as the negative ion. reactions are reversible and exothermic.Specifically, hydrogen reacts with lithium, sodium, potassium, rubidium,cesium, calcium, radium, strontium, francium, and barium, instoichiometric proportions to form hydrides.

. With the elements of Groups III-a (including the rare earth andactinide elements), lV-a and V-a, hydrogen forms pseudo-hydrides. Thesolubility of hydrogen in elements of these groups varies as the squareroot of the pressure, and it decreases with increase in temperature;Above about 300 C., palladium also behaves in this way. Elements ofthese groups are designated as Group B, the class consisting ofscandium, titanium, vanadium, ytterbiurn, zirconium, niobium, hafnium,tantalum, the rare earth metals (atomic numbers 57 through 71), and theactinide metals (atomic numbers 89 through 103); palladium being amember of this group at temperatures greater than about 300 C. Thissolution is commonly termed a hydridej though it is not a stoichiometriccompound.

My cO-pending application, Serial No. 815,406, (now I Patent No.3,122,728), illustrates a few of the many ways is a non-porouselectrically conductive tube, preferably of constant cross-sectionalarea. Suitable metals are nickel, pure iron (which is impermeable tomany gases), stainless steel, and molybdenum, for example. In any event,the inner surfaces of the tube D should not react with the materials itcontacts, including the gas involved. A typical sensor tube D ispreferably about 0.040 to 0.060" outside diameter with a wall thicknessof preferably about 0.005 to 0.015." Such tubes D are preferably abouttwo to thirty feet long, although they may be longer or shorter.

FIG. 4 shows a preferred form of transducing agent E enclosed in thesensor tube D. Here the transducing agent E is a filament 30, such aszirconium or titanium or calcium wire and may be about 0.025" to 0.050"in diameter, for example. A ribbon 31 of suitable material, such asmolybdenum, preferably about 0.020" wide and 0.002" thick, is Wrappedtightly around the filamentary transducing agent 30. The ribbon 31physically spaces the filament 30 from contact with the walls 32 of thetube D and prevents the transducing agent 30 from fusing or welding tothe tube walls 32, even in the event that the sensor A is exposed toextreme heat and even if the filament 30 is fully ingassed, so that itis enlarged to nearly the internal diameter of the tube D.

As a simplified example of installation of the sensor A of FIG. 4 to theresponder B, one end 33 (FIG. 3) of the tube D may be connected by agas-tight seal to the responder B, while the other end 34 of the tube Dis still open. This free end 34 may be connected to a vacuum pump andthe tube D pumped free of gas. Then the tube D is heated, and then .purehydrogen is forced in through the free end 34, the zirconium filament 30absorbing the hydrogen while it cools. The originally pure metal 30 isconverted into an ingassed hydride. The free end 34 is then sealed offas by inserting a wire 35 and fusing it to the tube D, and the device isready for operation.

FIG. 3 shows one preferred form of responder B. This responder Bcomprises a unit 40 and has two circular plates 41 and 42, of non-porousmetal, preferably molybdenum or Kovar," between which is bonded (as bybrazing) a thin metal (e.g., molybdenum or Kovar) flexible disc ofdiaphragm 43. (According to Handbook of Material Trade Names, 1953Edition, published by Industrial Research Service at Dover, NewHampshire, Kovar is a registered trademark for an alloy of 20% nickel,17% cobalt, 0.2% manganese, and the balance iron.) The plates 41 and 42are hermetically sealed together and are in electrical contact for theirfull peripheries and over a substantial margin, but in the center thediaphragm 43 has a generally spherical-segment depression 44 called ablister, which is free to move relative to the plates 41 and 42 andconstitutes the active or movable part of the diaphragm 43. Use of adiaphragm with a blister 44 makes possible the use of an upper plate 42with a planar lower surface 45 and gives a more predictable response,but other diaphragm structures may be used where feasible. The lowerplate 41 is formed with a recess 46 in its upper surface, and thediaphragm 43 divides the resultant cavity between the plates into tworegions or chambers 47 and 48. Since the lower region 47 communicateswith the sensor A, it may be called the sensor chamber. The other region48 is located on the opposite side of the diaphragm 43 from the sensorA; so it may be called the anti-sensor chamber. Of course, either plate41 or 42 may actually be made by brazing together several thin plates ofthe desired configuration, and the recess 46 may be provided by using astack of preformed thin washers over a disc.

The end 33 of the sensor tube D is joined to and hermetically sealed tothe lower plate 41, fitting within a hole 50. The region 47 is closedand sealed except for its communication with the lumen of the sensortube D;

so the inside of the sensor A and the sensor chamber 47 enjoy a commonatmosphere to the exclusion of any other.

A tube 51 of non-porous ceramic material or other nonporouselectrically-insulating material extends through a stepped opening 52provided by a metal tube 52a that is brazed into the upper plate 42flush with the surface 45, the tube 51 being hermetically sealed inplace with its lower end 53 flush with the bottom surface 45 of theplate 42. The hole 52 and tube 51 are preferably centered with respectto the blister 44. A metal electrode tip 54, preferably of palladium orother metal that actively outgasses hydrogen when heated in thetemperature range involved is provided as the lower end of a metal rod55, preferably of molybdenum, inside the tube 51, the electrode 54 beinga contact portion of the rod 55 that lies flush with (or very slightlybelow) the lower surface 45 of the plate 42.

If sufficient pressure is applied to the sensor side of the blister 44,the blister will be deflected and will make contact with the electrodeportion 54, and if the deflecting force is removed, the restoring forceof the blister 44 will return it to its relaxed position and thus breakcontact with the electrode portion 54. The force necessary to deflectthe blister 44 may be chosen by proper design to accommodate a widerange of values.

The outer end of the molybdenum rod 55 is drilled axially to provide areceptacle 56 within which fits the end of a nickel capillary tube 57,which is secured to the rod 55, as by a cuplat braze, at a locationshort of the lower end 58 of the receptacle. A hole 59 extends radiallythrough the wall of the receptacle 56 in between the receptacle end 58and the end of the tube 57. A cap 59a, preferably of Kovar ormolybdenum, is brazed to the ceramic tube 51 and to the capillary tube57, and the lengths of the tubes '51 and 57 and the rod 55 are carefullychosen to match the coeificients of expansion and the lengths of the twometal members 55 and 57 to the coefficient of expansion and the lengthof the member 51. It is important to keep the lower end 54 of thecontact rod 55 from moving above the surface of the plate 42. With therelative lengths of the molybdenum and nickel parts chosen so that theirexpansion and contraction exactly cancel those of the ceramic tube 51,whose c-oefficient of expansion lies between those of nickel andmolybdenum, this distance is easily maintained.

The cylindrical rod 55 of molybdenum fits fairly snugly into the bore ofthe ceramic tube 51, while still leaving suflicient clearance for gaspassage. The radial hole 59 enables passage of hydrogen gas or a mixtureof hydrogen and a noble gas, such as argon or neon, through thecapillary tube 57 into the ceramic tube 51. Hence, the nickel tube 57may be used to introduce gas under pressure into the anti-sensor chamber48 to provide any desired pressure there, with resultant effect on theresponse characteristics of the blister 44. -It may then be closed olfby inserting a wire 59b in its outer end and brazing it to the tube 57.Then the tube 57 may be brazed to an electrical jack or socket member60. Thus, when the blister 44 contacts the electrode 54, electriccurrent can pass from the blister 44 to the rod 55, the tube 57, and thesocket 60, to which the electric warning circuit C is connected.

A preferred electrical warning circuit C is shown in FIG. 2. It will beseen that a connector 61 engages the socket 60 and from it a lead 62extends to two lamps 63 and 64 in parallel with each other and in serieswith the lead 62 and a lead 65, which leads to one side of a battery 66.The other side of the battery 66 leads through a relay 67, and, by leads68 and 69, is connected to a terminal 70 on the sensor tube D, near theresponder B.

A test circuit F is also provided. A second terminal 71 on the far endof the sensor tube D is connected by a lead 72 to a test switch 73,which is connected to a second battery 74. The other side of the battery74 is connected through an ammeter 75 to one pole 76 of the relay 67.The pole 76 is normally closed against a contact 77 that is connected bya lead 78 to the leads 68 and 69. A second pole 80 connects anddisconnects leads 81 and 82 of a bell relay 83. The body D of the sensorA is a good electrical conductor, so that even with many feet of it thetotal resistance will be low, only about one to ten ohms. Thus anungrounded circuit is provided through the sensor body D between theterminals 70 and 71.

When the blister 44 is not in contact with the electrode 54, the circuitthrough the battery 66 is open, and it cannot light the lamps 63 and 64or ring the bell 85. Whenever there is a fire or heat condition such asto emit suflicient gas inside the sensor A, the pressure in the sensorchamber 47 builds up and closes the blister 44 against the electrode 54,closing the circuit through the battery 66 and lighting the signal lamps63 and 64 and ringing the bell 85.

A novel feature of the responder 40 is that the electrode tip 54 is ofmetal hydride or metal with dissolved hydrogen gas that emits that gaswhen heated; therefore, after a blister in contact with the tip 54begins to move away from the tip, it it moves so slowly as to causearcing, the resultant heat causes the palladium or other hydride to emithydrogen, thereby increasing the gas pressure in the anti-sensor chamber48 and snapping the blister 44 away from the electrode tip 54.

While the two-lamp, one-bell circuit is preferred, it will be apparentthat, instead, there may be only a single lamp. The important thing isthat there is an ungrounded circuit with a warning device in series withthe responder B and sensor body D. That is, in essence, the warningcircuit C. Two 2.5 volt lamps 63 and 64 and a 2.5 volt bell 85 arepreferred to a single lamp to help get a highcurrent, low-voltagecircuit, which is trouble free, because of the current-voltage valuesand because even when one lamp burns out, another is present to give thewarning.

For testing the circuit of FIG. 2, the switch 73 is closed. The sensorelement E is then heated electrically by the current passing from thebattery 74 directly through the metal tube D. I may, however, use othermeans for heating the tube D and the sensor E electrically, and one suchmethod will be discussed later with reference to FIGS. 13 and 14. Theheat is uniformly distributed along the sensor A, which normallycontains a noble gas (such as neon or argon) in addition to the hydrideE. The sensor A may be adjusted so that if all of it is above a certaincritical temperature, the expansion of the noble gas itself will sufliceto move the blister 44 against the electrode tip 54. This temperaturemay be termed the all-point. Then, if most of the sensor A is below thisall-point, the responder B may still be actuated by a rise of a portionthereof above the gas-emission point of the hydride E, by a desiredamount. For testing, the allpoint may be used, and when the temperatureof the sensor A reaches the all-point temperature for which it has beenset, the responder B completes the alarm circuit, lighting the warninglamps 63 and 64 and actuating the relay 67. The relay 67 then breaks thecurrent in the test circuit by moving the pole 76 away from the contact77. With the flow of current in the test circuit F stopped, the sensor Acools off, finally reaching the point at which the responder B opens thealarm circuit, releasing the relay 67. This restores the flow of currentin the test circuit F, so that the sensor A again heats up. The cycle isrepeated as long as the test switch 73 is kept closed.

The intermittent flashing of the warning lights 63, 64 during the testindicates that the system is in good order. If there is a break in thesensor A or a fault in some other part of the system, the Warning lamps63, 64 will not light during the test, indicating that something iswrong with the system. Since it is the gas pressure in the sensor Awhich actuates the responder B during the test cycle, this test methodgives a true test of the entire fire detector system by producing actualhigh temperature conditions in the sensor.

The test switch 73 may be kept closed at all times during flight, givinga continuous test, without in any way hampering the units effectivenessas a fire detector.

If a fire condition exists in the vicinity of the sensor A, then theresponder B keeps the alarm circuit C closed, and the warning lamps 63,64 burn continuously, indicating an excessive temperature condition.During the time the system is indicating a fire, the relay 67 preventscurrent from flowing in the test circuit F. Actually, the continuous useof this test circuit F may improve the response rate of the detector;since the sensor is maintained at a fairly high temperature all thetime, it takes less time for a fire to heat the sensor A up to the pointat which it gives a warning.

The environmental temperature of the sensor A determines how long ittakes for the sensor A to heat up when the test current is on and tocool off when the test current is off. The higher the environmentaltemperature is, the shorter the heating-up time and the longer thecoolingoff time. Therefore the average current, averaged over each testcycle, decreases as the environmental temperature is raised. If anammeter 75 with a long time-constant (highly damped) is placed in serieswith the test circuit F, as shown in FIG. 2, it will perform the properaveraging and can be calibrated to read the actual environmentaltemperature of the sensor directly.

If it is desired that a warning be given when the environmentaltemperature reaches some overheat point below the all-point temperature,the ammeter 75 may be fitted with contacts 75a and 75b so that anexternal warning circuit 750 including a battery 75d is closed when thecurrent indicated by the meter 75 drops below that corresponding to theoverheat temperature. Meters fitted with such contacts are commerciallyavailable.

If the fire detector is faulty for some reason, then the relay 67 in thealarm circuit C will not break the current in the test circuit F. Theaverage current indicated by the ammeter 75 will then rise to a highvalue, indicating that the system has failed. If desired, the additionalset of contacts 75a and 75b may be set to close the external circuit 75cwhen the current indicated by the meter 75 exceeds a certain value, inorder to give a warning that there is a fault in the system, or two setsof such contacts may be provided.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

I claim:

1. A very sensitive pressure-responsive device, including incombination: a housing; a metal diaphragm in said housing and dividingsaid housing into first and second chambers, said diaphragm having anarea whose peripheray is rigidly fixed to said housing, said area beingdeformed into a blister that flexes in response to pressure in saidfirst chamber, and an electrode supported by said housing in said secondchamber and electrically-insulated therefrom directly opposite andcentrally located with respect to said blister on the side thereof awayfrom which said blister is normally deflected and having a tip of metalof the type that outgasses hydrogen when heated, said metal tip beingingassed with hydrogen, whereby deflection of said blister to a positioncausing arcing between said tip and said electrode heats said tip andcauses it to outgas, increasing the pressure in said second chamber,thereby snapping said blister away from said electrode.

2. A very sensitive pressure-responsive device, including incombination: a housing; a metal diaphragm in said housing and dividingsaid housing into first and second chambers, said diaphragm having acircular area whose periphery is rigidly fixed to said housing, saidarea being deformed into a blister that flexes in response to pressurein said first chamber, and an electrode supported by said housing andelectrically-insulated therefrom directly opposite and centrally locatedwith respect to said blister on the side thereof away from which saidblister is normally deflected and having a palladium tip ingassed withhydrogen, whereby when arcing occurs between said blister and saidelectrode, said tip is heated, which thereupon emits hydrogen,increasing the pressure in said second chamber and snapping said blisteraway from said electrode.

3. A very sensitive pressure-responsive device, including incombination: a housing; a metal diaphragm in said housing and dividingsaid housing into first andsecond chambers, said diaphragm having aflexing area that flexes in response to pressure in said first chamber,and an electrode supported by said housing in said second chamber andelectrically-insulated therefrom directly opposite said flexing area andhaving a tip of metal ingassed with hydrogen and of the type thatoutgasses hydrogen when heated, whereby arcing between said tip and saidarea heats said tip so that it outgasses hydrogen and increases thepressure in said second chamber, thereby snapping said area away fromsaid electrode.

No' references cited.

BERNARD A. GILHEANY, Primary Examiner.

1. VERY SENSITIVE PRESSURE-RESPOSNIVE DEVICE, INCLUDING IN COMBINATION:A HOUSING; A METAL DIAPHRAGM IN SAID HOUSING AND DIVIDING SAID HOUSINGINTO FIRST AND SECOND CHAMBERS, SAID DIAPHRAGMI HAVINGAN AREA WHOSEPERIPHERY IS RIGIDLY FIXED TO SAID HOUSING, SAID AREA BEING DEFORMEDINTO A BLISTER THAT FLEXES IN RESPONSE TO PRESSURE IN SAID FIRSTCHAMBER, AND AN ELECTRODE SUPPORTED BY SAID HOUSING IN SAID SECONDCHAMBER AND ELECTRICALLY-INSULATED THEREFROM DIRECTLY OPPOSITE ANDCENTRALLY LOCATED WITH RESPECT TO SAID BLISTER ON THE SIDE THEREOF AWAYFROM WHICH SASID BLISTER IS NORMALLY DEFLECTED AND HAVING A TIP OF METALOF THE TYPE THAT OUTGASSES HYDROGEN WHEN HEATED, SAID METAL TIP BEINGINGASSED WITH HYDROGEN, WHEREBY DEFLECTION OF SAID BLISTER TO A POSITIONCAUSONG ARCING BETWEEN SAID TIP AND SAID ELECTRODE HEATS SAID TIP ANDCAUSES IT TO OUTGAS, INCREASING THE PRESSURE IN SAID SECOND CHAMBER,THEREBY SNAPPING SAID BLISTER AWAY FROM SAID ELECTRODE.